From a Catholic perspective, baptism is a sacrament that marks the beginning of a person's journey of faith and initiation into the Christian community. The Catechism of the Catholic Church states that "Baptism is the sacrament of faith. But faith needs the community of believers. It is only within the faith of the Church that each of the faithful can believe."
Scripture references for the sacrament of baptism include John 3:5, where Jesus tells Nicodemus that "Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God," and Acts 2:38, where Peter tells the crowd on the day of Pentecost that "Repent, and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins."
The Catholic Church recognizes the validity of baptisms performed by other Christian denominations, and thus an adult who is already baptized in another denomination but wishes to join the Catholic Church will typically not be baptized again. However, an adult who has never been baptized, or whose baptism is uncertain, would be received into the Church through the sacrament of baptism.
As for the confession of faith, the Catechism of the Catholic Church states that "Baptism is the foundation of the whole Christian life, the gateway to life in the Spirit, and the door which gives access to the other sacraments". The Church recognizes the freedom of the person, The adult who is being baptised may not be able to express the faith in words, but the faith is recognized by the church if the person is willing to receive the sacrament.
Therefore, from a Catholic perspective, an adult who does not articulate some form of confession of faith can still be baptized if they are willing to receive the sacrament and begin their journey of faith in the Christian community.